The present disclosure relates to methods and compositions for use in subterranean operations. More particularly, the present disclosure relates to methods of reducing the viscosity of subterranean treatment fluids.
Well services can include various types of treatments that are commonly performed in a wellbore or subterranean formation. As used herein, the word “treatment” refers to any treatment for changing a condition of a portion of a wellbore or an adjacent subterranean formation; however, the word “treatment” does not necessarily imply any particular treatment purpose.
Treatment fluids may be used in a variety of subterranean treatments, including, but not limited to, stimulation treatments and sand control treatments. One common production stimulation operation that employs a treatment fluid is hydraulic fracturing. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more cracks, or “fractures,” in the subterranean formation. The fracturing fluid may comprise particulates, often referred to as “proppant,” that are deposited in the fractures. The proppant particulates, inter alia, prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to the well bore. Once at least one fracture is created and the proppant particulates are substantially in place, the fracturing fluid may be “broken” (i.e., the viscosity is reduced), and the fracturing fluid may be recovered from the formation.
Maintaining sufficient viscosity in these treatment fluids is important for a number of reasons. Maintaining sufficient viscosity is important in fracturing and sand control treatments for particulate transport and/or to create or enhance fracture width. Also, maintaining sufficient viscosity may be important to control and/or reduce fluid-loss into the formation. Moreover, a treatment fluid of a sufficient viscosity may be used to divert the flow of fluids present within a subterranean formation (e.g., formation fluids, other treatment fluids) to other portions of the formation, for example, by “plugging” an open space within the formation. At the same time, while maintaining sufficient viscosity of the treatment fluid often is desirable, it also may be desirable to maintain the viscosity of the treatment fluid in such a way that the viscosity may be reduced at a particular time, inter alia, for subsequent recovery of the fluid from the formation.
To provide the desired viscosity, polymeric gelling agents may be added to the treatment fluids. Examples of commonly used polymeric gelling agents include, but are not limited to, guar gums and derivatives thereof, cellulose derivatives, biopolymers, polysaccharides, synthetic polymers, and the like. To further increase the viscosity of a treatment fluid, often the molecules of the gelling agent are “crosslinked” with the use of a crosslinking agent. Conventional crosslinking agents usually comprise a metal ion that interacts with at least two polymer molecules to form a “crosslink” between them.
At some point in time, e.g., after a viscosified treatment fluid has performed its desired function, the viscosity of the viscosified treatment fluid should be reduced. This is often referred to as “breaking the gel” or “breaking the fluid.” This can occur by, inter alia, reversing the crosslink between crosslinked polymer molecules, breaking down the molecules of the polymeric gelling agent, or breaking the crosslinks between polymer molecules. The use of the term “break” herein incorporates at least all of these mechanisms. Certain breakers that are capable of breaking treatment fluids comprising crosslinked gelling agents are known in art. For example, breakers comprising sodium bromate, sodium chlorite, and other oxidizing agents have been used to reduce the viscosity of treatment fluids comprising crosslinked polymers. Examples of such breakers are described in U.S. Pat. No. 5,759,964 to Shuchart, et al., and U.S. Pat. No. 5,413,178 to Walker, et al., the relevant disclosures of which are herein incorporated by reference.
After completion of a hydraulic fracturing operation on a well, residual fracturing fluid left over in the fracture may reduce the permeability of the well formation, thereby also decreasing the production efficiency of the well. Thus, before a well that has undergone hydraulic fracturing begins production, the fracturing fluid is typically treated to increase formation permeability. In order to reduce the negative effect of fracturing fluid, oxidizers such as sodium persulfate (SP), ammonium persulfate, coated breakers, enzyme breakers, and delayed acid generators have been used to reduce the viscosity of the fracturing fluid and cause an increase in formation permeability.
In addition, residual fracturing fluid may cause damage to a well formation after a hydraulic fracturing operation is completed. Removal of the fracturing fluid allows greater control and protection of formation integrity. Greater stability of the formation lowers the risk that shifts or changes in the formation will cause some disruption to production or damage to equipment. Thus, efficient clean-up of the fracturing fluid generates an added benefit to production efficiency.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.